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/*
* Copyright 2016 WebAssembly Community Group participants
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
//
// Removes module elements that are are never used: functions and globals,
// which may be imported or not.
//
#include <memory>
#include "wasm.h"
#include "pass.h"
#include "ast_utils.h"
namespace wasm {
enum class ModuleElementKind {
Function,
Global
};
typedef std::pair<ModuleElementKind, Name> ModuleElement;
// Finds reachabilities
struct ReachabilityAnalyzer : public PostWalker<ReachabilityAnalyzer> {
Module* module;
std::vector<ModuleElement> queue;
std::set<ModuleElement> reachable;
ReachabilityAnalyzer(Module* module, const std::vector<ModuleElement>& roots) : module(module) {
queue = roots;
// Globals used in memory/table init expressions are also roots
for (auto& segment : module->memory.segments) {
walk(segment.offset);
}
for (auto& segment : module->table.segments) {
walk(segment.offset);
}
// main loop
while (queue.size()) {
auto& curr = queue.back();
queue.pop_back();
if (reachable.count(curr) == 0) {
reachable.insert(curr);
if (curr.first == ModuleElementKind::Function) {
// if not an import, walk it
auto* func = module->checkFunction(curr.second);
if (func) {
walk(func->body);
}
} else {
// if not imported, it has an init expression we need to walk
auto* glob = module->checkGlobal(curr.second);
if (glob) {
walk(glob->init);
}
}
}
}
}
void visitCall(Call* curr) {
if (reachable.count(ModuleElement(ModuleElementKind::Function, curr->target)) == 0) {
queue.emplace_back(ModuleElementKind::Function, curr->target);
}
}
void visitCallImport(CallImport* curr) {
if (reachable.count(ModuleElement(ModuleElementKind::Function, curr->target)) == 0) {
queue.emplace_back(ModuleElementKind::Function, curr->target);
}
}
void visitGetGlobal(GetGlobal* curr) {
if (reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0) {
queue.emplace_back(ModuleElementKind::Global, curr->name);
}
}
void visitSetGlobal(SetGlobal* curr) {
if (reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0) {
queue.emplace_back(ModuleElementKind::Global, curr->name);
}
}
};
struct RemoveUnusedModuleElements : public Pass {
void run(PassRunner* runner, Module* module) override {
std::vector<ModuleElement> roots;
// Module start is a root.
if (module->start.is()) {
roots.emplace_back(ModuleElementKind::Function, module->start);
}
// Exports are roots.
for (auto& curr : module->exports) {
if (curr->kind == ExternalKind::Function) {
roots.emplace_back(ModuleElementKind::Function, curr->value);
} else if (curr->kind == ExternalKind::Global) {
roots.emplace_back(ModuleElementKind::Global, curr->value);
}
}
// For now, all functions that can be called indirectly are marked as roots.
for (auto& segment : module->table.segments) {
for (auto& curr : segment.data) {
roots.emplace_back(ModuleElementKind::Function, curr);
}
}
// Compute reachability starting from the root set.
ReachabilityAnalyzer analyzer(module, roots);
// Remove unreachable elements.
{
auto& v = module->functions;
v.erase(std::remove_if(v.begin(), v.end(), [&](const std::unique_ptr<Function>& curr) {
return analyzer.reachable.count(ModuleElement(ModuleElementKind::Function, curr->name)) == 0;
}), v.end());
}
{
auto& v = module->globals;
v.erase(std::remove_if(v.begin(), v.end(), [&](const std::unique_ptr<Global>& curr) {
return analyzer.reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0;
}), v.end());
}
{
auto& v = module->imports;
v.erase(std::remove_if(v.begin(), v.end(), [&](const std::unique_ptr<Import>& curr) {
if (curr->kind == ExternalKind::Function) {
return analyzer.reachable.count(ModuleElement(ModuleElementKind::Function, curr->name)) == 0;
} else if (curr->kind == ExternalKind::Global) {
return analyzer.reachable.count(ModuleElement(ModuleElementKind::Global, curr->name)) == 0;
}
return false;
}), v.end());
}
module->updateMaps();
}
};
Pass* createRemoveUnusedModuleElementsPass() {
return new RemoveUnusedModuleElements();
}
} // namespace wasm
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